Hydroealkylation process and catalyst

ABSTRACT

Alkylaromatics are hydrodealkylated to aromatics by passage with hydrogen over a supported catalyst of nickel and a Group Ib or IIb metal promoter at elevated temperatures.

0 United States Patent [151 3,666,824 Jenkins 1 May 30, 1972 [5 HYDROEALKYLATION PROCESS AND [56] References Cited CATALYST UNITED STATES PATENTS [72] In ent John Je ns, S b ook, 3,233,002 2/1966 Kovach et a1. ..260/672 3,291,850 12/1966 Carson "260/672 [73] Ass'gnee' New 3,435,084 3/1969 Cabbage et a]. ..260/672 [22] Filed: May 20, 1970 Primary ExaminerCurtis R. Davis [21] Attamey-John l-l. Colvin and Henry c. Geller ABSTRACT Alkylaromatics are hydrodealkylated to aromatics by passage [52] U.S. Cl. ...260/672 R with hydrogen over a supported catalyst of nickel and a Group [51] Int. Cl ....C07c 3/58 lb or llb metal promoter at elevated temperatures. [58] Field of Search ..260/672 6 Claims, No Drawings HYDROEALKYLATION PROCESS AND CATALYST BACKGROUND OF THE INVENTION This invention relates to a process for the catalytic conversion of hydrocarbons and relates more particularly to a process for the hydrodealkylation of alkylaromatics.

Aromatic hydrocarbons such as benzene and naphthalene and their alkyl derivatives are important raw materials used in the chemical and related industries for the preparation of valuable products. For many years the primary source of such aromatic hydrocarbons was the coal tar industry. More recently, however, the petroleum industry has become a leading source for these materials. This has resulted primarily from the availability of the catalytic reforming process, wherein naphthene hydrocarbons are dehydrogenated to produce a reformate rich in aromatics, and more efficient processes for separating the aromatic hydrocarbons from the reformate.

The supply and demand relationship among the individual aromatic hydrocarbons varies. For example, toluene may be in large supply while benzene may be in short supply. To correct such imbalances and to provide flexibility, it is a common practice to convert toluene to benzene or alkylnaphthalenes to naphthalene by one of a variety of well known processes. One known method of interconverting aromatics is catalytic disproportionation, wherein, for example toluene is disproportionated to benzene and xylenes. However, this approach has met with little success because the catalysts employed are generally too low in activity or lead to excessive side reactions.

Another, more commonly employed, method for converting alkyl benzenes and alkylnaphthalenes to benzene and naphthalene respectively is catalytic hydrodealkylation wherein a mixture of an alkylaromatic and hydrogen is contacted at elevated temperatures and pressures with a catalyst to give aromatic hydrocarbons and methane. Catalysts employed heretofore include the noble metals, such as platinum and palladium, which have the disadvantage of being inhibitively expensive. Other metals, for example molybdenum, copper, cadmium, tin and lead, have also been employed, both in massive and supported forms but have the disadvantage of requiring high hydrodealkylation reaction pressures (oflen over 1,000 psi) and temperatures usually over 1,000 F) and giving low selectivities to desired aromatics.

STATEMENT OF THE INVENTION It has now been found that alkylaromatics are hydrodealkylated to aromatics (e.g., toluene to benzene, and alkylnaphthalene to naphthalene) in high selectivity by contact with certain promoted supported nickel catalysts at relatively low temperatures and pressures. In accordance with the process of the invention, alkylaromatics having from seven to about 15 carbon atoms are contacted in the presence of added hydrogen at a temperature in the range from about 250 to 600 C, at a pressure of from about to about 250 psig and at a weight hourly space velocity of from about 0.5 to 5.0 with a catalyst comprising nickel and Group lb or Ilb metal promoter on a porous inert support.

DESCRIPTION OF PREFERRED EMBODIMENTS Catalyst The catalyst composite contains nickel and at least one metal promoter selected from the metals of the lb and llb groups of the Periodic Table on a porous inert support. Both the nickel and the Group lb or llb promoters are generally present on the support as oxides.

The amount of nickel calculated as metal present in the catalysts of the invention may vary from as low as about 1 percent by weight to as high as about 25 percent by weight of the total composition. Usually, the concentration of nickel in the catalyst is within the range of from 3 to percent by weight of the total catalyst. When certain preferred Group lb and llb metal promoters are employed, it is most suitable to have nickel present in the catalyst composition in the amount of from 5 to 10 percent by weight of the total composition.

Although all the Group Ib and llb metals of atomic number 29 to 80, inclusive, (copper, silver, gold, zinc, cadmium and mercury) are efiective promoters in hydrodealkylation catalysts in accordance with this invention, those of atomic number 29-47 (copper, silver and zinc) are preferred. Catalysts containing copper as promoter are especially preferred. Generally, the use of only one Group lb or llb promoter is suitable, but, if desired, the combination of two or more promoters may be employed.

On a weight basis, it is generally suitable to add from about 1 to about [0 percent by weight of Group lb or llb promoters (calculated as metal) based on the total catalyst composition. On a gram-atom basis, it is very suitable to add not more than about 1 gram-atom of promoter for each gram-atom of nickel present on the catalyst, with nickel to promoter mol ratios of from about 1 to l to about to 1 being preferred. When the preferred Group lb and Ilb metal promoters, copper, zinc and silver, are employed, nickel to promoter mol ratio of from 1.2 to l to about 10 to 1 give excellent results. As a general rule, increasing the amount of promoters leads to higher selectivity to desired aromatics but lower activity, while increasing the nickel content gives higher catalyst activity but oflen lower selectivities. Most preferred catalysts contain from 5 to 10 percent by weight of nickel and from 1 to 6 percent by weight of copper, on a porous inert support, such amounts of copper and nickel being selected to give a molar ratio of nickel to copper offrom 1.2 to l to 10 to 1.

Supports for catalysts useful in accordance with this invention can be selected at will from the large number of conventional porous inert refractory oxide carriers or support materials. Such conventional support materials may be of natural or synthetic origin and of microporous structure. They may have the shape of fine particles, chunks, pieces, pellets, rings, spheres, and the like. 'Very suitable supports comprise those of siliceous and/or aluminous compositions. Representative examples of suitable supports are the aluminum oxides, pumice, zirconia, magnesia, kieselguhr, Titania silica, ceramics, fire brick, and the like. Particularly useful supports comprise the inert, porous, high surface area aluminous and siliceous materials, in particular the inert aluminous and siliceous materials having surface areas above about 10 m /g. Preferred as support are silicas, silica-aluminas, and aluminas having surface areas of from about 50 to about 1,000 m /g, with silicas and aluminas having surface areas of from 100 to 1,000 m /g being most preferred.

The catalysts can be prepared by a variety of conventional catalyst preparation methods, for example a slurry or powder of finely divided nickel and Group lb or llb metal, either as metals or oxides, may be applied to a suitable shaped support and thereafter calcined. In another method, the catalytic metals in powder form are combined with unshaped support material and then shaped and calcined.

It is preferred to employ an impregnation process for preparation of the catalysts. That is, a process having the consecutive steps of impregnating a suitable inert porous catalyst support with a solution of soluble compounds of catalytic and promoter metals, optionally subjecting the resulting impregnated support to drying under relatively mild temperature conditions to remove absorbed solvent and then heating the dried impregnated support, under calcining conditions at a temperature of at least 250 C, in the presence of an oxygencontaining gas. Although organic-solvented solutions of soluble metal salts may be employed for impregnation, for example an ethylene glycol solution of cupric acetate and nickel acetate, it is generally more convenient to use aqueous impregnation solutions. Any appropriate water-soluble salt of nickel and Group lb or llb metals may be used, for example nitrates, chlorides and the like. The presence of sulfates should, however, be avoided. Two catalyst preparation techniques are preferred. In one, a shaped support is impregnated with a single solution containing soluble salts of both nickel and Group lb or llb metal promoter, optionally dried and then calcined in air at from 400600 C to convert the catalytic metals to oxides. In the other, the support is first impregnated with a solution of nickel salt optionally dried and then calcined in air at 400-600 C and thereafter impregnated with an aqueous solution of promoter, optionally dried, and then calcined in air at 400-600 C. When promoter is put on the support before the nickel a less desirable catalyst often results.

I-Iydrodealkylation Process Feed for the process of the invention can be a substantially pure alkylaromatic hydrocarbon having from seven to 15 carbon atoms, mixtures of such alkylaromatics, or hydrocarbon fractions rich in alkylaromatics. Feeds include monoand dicyclic (including fused ring) aromatics, that is, the alkylbenzenes, alkyldiphenyls, and alkylnaphthalenes. It is preferred that any alkyl group has no more than four carbon atoms. Toluene is a preferred monocyclic alkylaromatic feed while monoalkylnaphthalenes having no more than four carbon atoms in the alkyl group are preferred di-cyclic alkylaromatic feedstocks. In the hydrodealkylation reaction the alkylaromatic is converted to a corresponding unsubstituted (or less substituted) aromatic hydrocarbon. For example, toluene is converted to benzene and methylnaphthalene is converted to naphthalene.

In the process of the invention the alkylaromatic feedstock and hydrogen are contacted with Group Ib-IIb metalpromoted nickel catalyst at a temperature in the range of from about 250 to 600 C, usually 275 to 500 C and preferably from about 300 to 450 C. In general, the rate of hydrodealkylation is increased as temperature is increased.

One mole of hydrogen is consumed per mole of mon-alkylaromatic reacted in the hydrodealkylation reaction. It is advantageous to employ an excess of hydrogen over this molar amount; for example, it has been observed that the rate of hydrodealkylation of alkylaromatics increases in proportion to the increase of hydrogen. A molar ratio of hydrogen to alkylaromatic, commonly referred to as a hydrogen to oil mole ratio, offrom l to l to 25 to I, usually from 1 to l to 10 to I, and preferably from 1 to 1 to 4 to l is employed.

Diluents, such as hydrocarbons, nitrogen, argon, steam or the like may suitably be present in the reaction feedstocks or may be purposefully added to the hydrodealkylation mixture.

The total reaction pressure required in the process is relatively very low. The process may be carried out at pressures as low as about 5 pounds per square inch gauge (psig). In no case are pressures markedly above 250 psig necessary. Total reaction pressures of from l0 to 100 psig are preferred.

The hydrodealkylation reaction is effected over a wide range of space velocities. In general, the process of the invention is conducted at a space velocity in the range of from about 0.5 to about and preferably from 1.0 to 4.0. Space velocity, as the term is used herein, abbreviated to WHSV, is expressed as weight of feed per hour per unit weight of catalyst. In general, conversion is decreased as space velocity is increased.

EXAMPLE 1 Six hydrodealkylation catalysts (Catalysts A to F) were prepared by impregnating a high surface area, high purity, porous silica gel (Davidson grade 950 silica gel surface area about 850 m lg, void volume 0.4 cc/g) with aqueous solution of nickel nitrate. In five of these six preparations, copper nitrate was added to the impregnating liquid. The impregnations were carried out at room temperature. The catalysts were drained and then dried for 16 hours at 120 C in an air oven and then heated in air for 1 hour at 565 C to convert the nitrates to oxides. The total metal content was 10 percent by weight for all catalysts.

TABLE I Nickel Content, Copper Content, Nickel to %w Calcd as %w Calc'd as Promoter Catalyst Ni metal Cu metal mol ratio B 9 1 9.7 to 1 C 8 2 4.3 to l D 6 4 1.62 to l E 4 6 0.72 to 1 F 2 8 0.27 m l EXAMPLE [I The six materials of Example I were tested as hydrodealkylation catalysts. In a control experiment, 8.7 grams of catalyst A, the nickel catalyst containing no copper, was placed in the center heated section of a 15 inch i.d. tubular reactor 12 inches long. The catalyst was heated to 300 C in an atmosphere of flowing hydrogen at 0 psig, the pressure raised to 20 psig, and hydrogen and reagent grade toluene then were passed over the catalyst. The reaction temperature was now 400 C, total pressure was 20 psig, hydrogen to oil ratio 2, WHSV 2.0 pounds of toluene/pound of catalyst/hour. The reaction products were collected and analyzed by gas chromatography. Basis the weight of toluene charged, the following products were recovered:

Methane 24.3 %w C,-C 0.1 %w Benzene 13.4 %w Toluene 670 %w This conversion was 33 percent and molar selectivity to benzene was 48 percent.

Identical runs were made with catalysts B to F, and the results are given in Table II.

TABLE II Catalyst Toluene Conversion, Selectivity to Benzene,

% mole B 58.2 73 C 62.5 78 D 27.5 87 E 9.9 84 F 13.4 98 33 47 EXAMPLE III A series of catalysts were prepared and tested to demonstrate the use of otherGroup lb or lIb metals as promoters.

The methods of Examples I and II were employed for preparation and testing. The results are given in Table III. Comparable results for the preferred nickel-copper catalysts are also shown. For all catalysts the yield of benzene passes through a maximum as the promoter concentration is increased, however, the selectivity increases continuously.

copper 10.0 0

90 silver 1.0 27 8 .0 silver 2.0 16 9.7 zinc 0.3 27 9.3 zinc 0.7 27 9.0 nnc 1.0 17 8.0 zinc 2.0 3

I claim as my invention:

1. A process for hydrodealkylating an alkylaromatic hydrocarbon of from seven to about carbon atoms per molecule which comprises contacting the alkylaromatic hydrocarbon and hydrogen in a hydrodealkylation reaction zone at a temperature in the range of from about 275 to about 500 C with a catalyst composite consisting essentially of 3 to 15 percent by weight of nickel and from 1 gram-atom to 0.01 gram-atom per gram-atom of nickel of a Group lb or Ilb metal promoter on a porous inert refractory oxide support and recovering the dealkylated aromatic hydrocarbon from the reaction product.

2. The process in accordance with claim 1 wherein the contacting is conducted in the presence of from about 1 to about moles of hydrogen per mole of alkylaromatic at a pressure in the range from about 5 psi to about 250 psi.

3. The process in accordance with claim 2 wherein the Group lb or lIb metal is copper.

4. A process for the hydrodealkylation of toluene to benzene which comprises contacting toluene and from 1 to 10 moles of hydrogen per mole of toluene in a hydrodealkylation reaction zone at a temperature in the range of from about 300 to about 450 C, at a pressure in the range of from 5 psi to 250 psi, and at a weight hourly space velocity of from 05 to about 10.0 hr, with a catalyst composite consisting essentially of from 5 to 10 percent by weight of nickel and from I to 10 percent by weight of copper, said percent by weight of copper being selected to give a molar ratio of nickel to copper on the catalyst of from 1.2 to l to 10 to l, on an inert porous refractory oxide support and recovering benzene from the reaction product.

5. The process in accordance with claim 4 wherein the inert porous refractory oxide support consists essentially of silica and has a surface area of from mlg to 1,000 m lg.

6. The process in accordance with claim 4 wherein the inert porous refractory oxide support consists essentially of alumina and has a surface area of from 100 m lg to 1,000 m lg. 

2. The process in accordance with claim 1 wherein the contacting is conducted in the presence of from about 1 to about 25 moles of hydrogen per mole of alkylaromatic at a pressure in the range from about 5 psi to about 250 psi.
 3. The process in accordance with claim 2 wherein the Group Ib or IIb metal is copper.
 4. A process for the hydrodealkylation of toluene to benzene which comprises contacting toluene and from 1 to 10 moles of hydrogen per mole of toluene in a hydrodealkylation reaction zone at a temperature in the range of from about 300* to about 450* C, at a pressure in the range of from 5 psi to 250 psi, and at a weight hourly space velocity of from 0.5 to about 10.0 hr 1, with a catalyst composite consisting essentially of from 5 to 10 percent by weight of nickel and from 1 to 10 percent by weight of copper, said percent by weight of copper being selected to give a molar ratio of nickel to copper on the catalyst of from 1.2 to 1 to 10 to 1, on an inert porous refractory oxide support and recovering benzene from the reaction product.
 5. The process in accordance with claim 4 wherein the inert porous refractory oxide support consists essentially of silica and has a surface area of from 100 m2/g to 1,000 m2/g.
 6. The process in accordance with claim 4 wherein the inert porous refractory oxide support consists essentially of alumina and has a surface area of from 100 m2/g to 1,000 m2/g. 